In printing, copying, duplicating and like machines, copy sheets are fed through various stations of the machine individually and, often, at a high rate of speed. In some machines, the copy sheets are fed individually in a seriatim fashion (i.e. individually with spacing between the sheets) through the machine for copying purposes. For instance, the sheets may be fed individually from a stack of sheets at an in-feed station over a conveyor board to a registration station prior to feeding the sheets into the cylinders of the printing couple of the machine. Particularly in high speed machines, some type of "holddown" system is used to keep the sheets flat on the conveyor board. For instance, some machines operate at a rate of as much as 10,000 or more sheets per hour, and the sheets have a tendency of literally "flying" off of the conveyor board due to their light weight against air resistance. Consequently, some form of system usually is incorporated to hold the sheets down onto a subjacent support surface, such as a conveyor board.
Various holddown systems have used such mechanisms as cam surfaces for engaging the upper side edges of the copy sheets, sometimes with an overhead roller for engaging the sheets approximately on the centerline of their upper surfaces. Such mechanical systems may function satisfactorily in relatively slow machines, but mechanical systems often are insufficient in high speed machines. Air jet systems have been used in some high speed machines, but such systems often encounter problems in timing the air jets with the seriatim timing of the passing sheets. Some systems employ a combination of mechanical means and air jet means, but the drawbacks of either type of system still are present.
In still other machines, vacuum means have been employed as a copy sheet holddown medium. The problem with a vacuum system is its inherent nature of not being capable of rapid cycling, as with a pulsed air jet, and any leakage between sheets bleeds off the vacuum. Consequently, some machines feed the copy sheets in an interleaved array (i.e. whereby the leading and trailing edges of the sheets overlap). A continuous vacuum therefore can be employed because there is n spacing between the sheets which otherwise would bleed the vacuum means. This type of feeding system creates still further problems because it is not as easy to register interleaved copy sheets as it is to register individual copy sheets which are fed in a seriatim manner.
This invention is directed to solving the above problems and dilemmas by providing a new and improved copy sheet feeding system which employs vacuum means as the copy sheet holddown medium, the system being readily applicable for feeding sheets individually in seriatim fashion.